1. Field of the Invention
This invention pertains to a device for use in the treatment of glaucoma, and more particularly to a drainage device implanted to lower the intraocular pressure of the eye by filtration.
2. Brief Description of Related Art
Glaucoma is a condition of the eye wherein the intraocular pressure is abnormally high. If this condition persists the optic nerve is damaged. It was discovered that glaucoma could be surgically treated by providing a drain to continuously withdraw excess aqueous humor fluid from the anterior chamber of the eye (glaucoma filtration surgery). Initially, this fluid was allowed to drain into the extraocular eye tissues; see for example U.S. Pat. No. 4,037,604. However, a problem with this approach was that over a period of time the surgical site was covered by fibrous scar tissue which occluded the drainage opening. In order to overcome this problem a band was proposed which covered the drainage hole to protect it from scar tissue; see A Long Krupin-Denver Valve Implant Attached to a 180.degree. Scleral Explant for Glaucoma Surgery, Krupin et al. Ophthalmology Vol. 95, No. 9, September 1988, pp. 1174-1180.
In U.S. Pat. No. 4,457,757 to Molteno, instead of a band covering the drainage site a circular plate of uniform radius is used, having a convex face which faces away from the eye. The convex face of the plate receives a tube draining the anterior chamber of the eye. One or more additional round plates of uniform radius may be provided, which are coupled to the first plate and each other by secondary distribution tubes in a "daisy chain" fashion, because each plate individually may not have a sufficient capacity to hold a volume of drainage fluid sufficient to reduce intraocular pressure effectively. A problem with the multiple plate, daisy-chain structure is that it can drain the eye too fast, resulting in hypotony (a very low intraocular pressure) and a flattened anterior chamber. This condition makes further surgery more difficult and is disadvantageous to the patient since vision is impaired until normal pressure is restored (which may require several weeks). A further disadvantage is that the circular plates are fabricated of relatively hard material (i.e.; polypropylene) which must be solidly anchored in place on the eye sclera by four or more sutures spaced around the outer periphery of the plates.
In U.S. Pat. No. 4,750,901 (again to Molteno) an attempt was made to alleviate the problem of hypotony described above by placing a barrier or partition wall on the convex surface of the circular plate. Of course, this sub-dividing structure (to retard drainage) complicates fabrication and is difficult to mold. Moreover, multiple circular plates may still be required to insure a sufficient capacity for the drainage fluid.
In view of the above-mentioned disadvantages of the prior art, it is an objective of the present invention to provide a drainage device which consists of a single oval (elongate) plate having a capacity and surface area large enough to accommodate the drainage fluid, without encouraging hypotony.
Another objective is to provide a drainage device which is readily implanted and secured to the eye sclera by surgeons who have received minimum training and experience in similar implantations.
A further objective is to provide a drainage device with an integral and simple means of avoiding depressurizing the eye too fast.
Yet another objective is to provide a drainage device which is easy and economical to manufacture.
Other objectives and advantages of the invention shall become apparent from the following description of the invention.